The present invention relates to light wood-base materials comprising from 30 to 95% by weight, based on the wood-base material, of wood particles, the wood particles having a mean density of from 0.4 to 0.85 g/cm3, from 2.5 to 20% by weight, based on the wood-base material, of polystyrene and/or of styrene copolymer as a filler, the filler having a bulk density of from 10 to 100 kg/m3, and from 2.5 to 50% by weight, based on the wood-base material, of a binder, the mean density of the light wood-base material being less than or equal to 600 kg/m3.
Wood-base materials constitute an economical and resource-saving alternative to solid wood and are very important particularly in furniture construction, in laminate floors and as building materials. Wood particles of different thickness, e.g. wood chips or wood fibers from various timbers, serve as starting materials. Such wood particles are usually pressed with natural and/or synthetic binders and, if appropriate, with addition of further additives to give board-like or strand-like wood-base materials.
The industrial demand for light wood-base materials has increased steadily in recent years, in particular since take-away furniture has gained in popularity, i.e. the cash payment and self-collection of furniture by the end customer. Furthermore, the increasing oil price which leads to a continual increase in, for example, the transport costs, has given rise to a greater interest in light wood-base materials.
In summary, light wood-base materials are of considerable importance for the following reasons:
Light wood-base materials lead to simpler handling of the products by the end customers, for example in packing, transporting, unpacking or assembly of the furniture. Light wood-base materials lead to lower transport and packaging costs; furthermore, material costs can be reduced in the production of light wood-base materials. For example, when used in means of transport, light wood-base materials can lead to lower energy consumption of these means of transport. Furthermore, with the use of light wood-base materials, for example, material-consumptive decorative parts, such as thicker worktops and side panels in the kitchen, which are currently fashionable, can be offered more economically.
The prior art includes a wide range of proposals for reducing the density of the wood-base materials.
For example, tubular particle boards and honeycomb boards may be mentioned as light (wood-base) materials. Owing to their particular properties, tubular particle boards are used mainly as an inner layer in the production of doors. Disadvantages of these materials are the insufficient resistance to screw extraction, the complicated fixing of fittings and the difficulties in edging.
Furthermore, the prior art includes proposals for reducing the density of wood-base materials by additives to the glue or to the wood particles.
CH 370229 describes light and simultaneously pressure-resistant compression-molded materials which consist of woodchips or fibers, a binder and a porous plastic serving as a filler. For the production of the compression-molded materials, the woodchips or fibers are mixed with a binder and foamable or partly foamable plastics, and the mixture obtained is molded at elevated temperature. Binders which may be used are all conventional binders suitable for the gluing of wood, such as, for example, urea-formaldehyde resins. Suitable fillers are foamable or already foamed plastic particles, preferably expandable thermoplastics, such as styrene polymers. The particle size of the plastics used is in general from 0.6 to 10 mm in the case of prefoamed plastics. The plastics are used in an amount of from 0.5 to 5% by weight, based on the woodchips. The boards described in the examples have a density of from 220 kg/m3 to 430 kg/m3 and a mean flexural strength of from 3.6 N/mm2 to 17.7 N/mm2 at a thickness of from 18 to 21 mm. The transverse tensile strengths are not stated in the examples.
WO 02/38676 describes a process for the production of light products in which from 5 to 40% by weight of foamable or already foamed polystyrene having a particle size of less than 1 mm, from 60 to 95% by weight of lignocellulose-containing material and binder are mixed and are molded at elevated temperature and elevated pressure to give the finished product, the polystyrene melting and firstly impregnating the lignocellulose-containing material and secondly by migration to the surface of the product, forming a hard, water-resistant skin. The binder used may be, inter alis, urea-formaldehyde resin or melamine-formaldehyde resin. In the example, a product having a thickness of 4.5 mm and a density of 1200 kg/m3 is described.
US 2005/0019548 describes light OSB boards with the use of fillers having a low density. Binders described are polymeric binders, for example, diphenylmethane 4,4-diisocyanate resin. Fillers described are glass, ceramic, perlite and polymeric materials. The polymeric material is used in an amount of from 0.8 to 20% by weight, based on the OSB board. The material Dualite, which consists of polypropylene, polyvinylidene chloride or polyacrylonitrile, is used as polymeric material in the examples. A weight reduction of 5% is described. In the examples, OSB boards having a density of from 607 to 677 kg/m3 and a transverse tensile strength of from 0.31 to 0.59 N/mm2 are described.
US 2003124443 discloses a material which consists of woodchips, binder and fillers. Fillers mentioned are, inter alia, polymers based on styrene. The volume ratio of the woodchips to the binder is advantageously 1:1. Furthermore, boards from the prior art are described in which the volume ratio of binder to woodchips is 90:10. These boards from the prior art have a density of 948 kg/m3. Binders described are, inter alia, thermosetting resins. Examples according to the invention describe boards which have a volume ratio of binder to woodchips of 45:55 and a density of 887 kg/m3.
JP 06031708 describes light wood-base materials, a mixture of 100 parts by weight of wood particles and from 5 to 30 parts by weight of particles of synthetic resin foam being used for the middle layer of a three-layer particle board, these resin particles having a density of not more than 0.3 g/cm3 and a compressive strength of at least 30 kg/cm2. It is furthermore stated that the specific density of the wood particles should not exceed a value of 0.5 g/cm3.
In the examples, a mechanical strength of the wood-base materials produced of from 4.7 to 4.9 kg/cm3 is achieved with the use of wood particles from Japanese cedar having a density of 0.35 g/cm3. With the use of lauan and kapur wood particles having a mean density of 0.6 g/cm3, it was possible to achieve only a mechanical strength of the wood-base materials produced of 3.7 kg/cm3.
In summary, the disadvantage of the prior art is that firstly the light (wood-base) materials described have insufficient mechanical strengths for furniture production, such as, for example, insufficient resistance to screw extraction. Secondly, the wood-base materials described in the prior art still have a high density of not more than 600 kg/m3. Furthermore, timbers having a density of less than 0.5 g/cm3 which is unusually light for the European market, are used in the prior art for the production of light wood-base materials.
Insufficient mechanical strength can lead, for example, to breaking or tearing of the components. Furthermore, these components tend to exhibit additional flaking off from further wood material on drilling or sawing. In the case of these materials, the fastening of fittings is more difficult.